Application InterfaceΒΆ

The WSGI application interface is implemented as a callable object: a function, a method, a class or an instance with an object.__call__() method. That callable must:

  1. accept two positional parameters:
  • A dictionary containing CGI like variables; and
  • a callback function that will be used by the application to send HTTP status code/message and HTTP headers to the server.
  1. return the response body to the server as strings wrapped in an iterable.

The application skeleton:

# The application interface is a callable object def application ( # It accepts two arguments: # environ points to a dictionary containing CGI like environment # variables which is populated by the server for each # received request from the client environ, # start_response is a callback function supplied by the server # which takes the HTTP status and headers as arguments start_response ): # Build the response body possibly # using the supplied environ dictionary response_body = 'Request method: %s' % environ['REQUEST_METHOD'] # HTTP response code and message status = '200 OK' # HTTP headers expected by the client # They must be wrapped as a list of tupled pairs: # [(Header name, Header value)]. response_headers = [ ('Content-Type', 'text/plain'), ('Content-Length', str(len(response_body))) ] # Send them to the server using the supplied function start_response(status, response_headers) # Return the response body. Notice it is wrapped # in a list although it could be any iterable. return [response_body]

This code will not run because it lacks the server instantiation step. Next page will show how to do it.